Indeed, the question came up at the news conference itself.
AP reporter Jonathan Lemire courageously asked "does the Russian Government have any compromising material on President Trump or his family?"
Think of how extraordinary - how unprecedented - that moment was.
Can you imagine a similar question being asked about any previous US president? I can't.
In the past, the only people who questioned the loyalty of US presidents were crazy conspiracy theorists such as the John Birchers, who accused President Dwight Eisenhower of being a Russian agent - or the birthers, including Trump, who questioned whether President Barack Obama was really born in the United States.
But today the question of where the President's loyalties lie is a legitimate one, and it will only grow in urgency after Putin deflected the question about whether he had kompromat on Trump.
The Russian President dismissed the issue as "nonsense," but it was his answer that was nonsensical.
Putin said that he was not even aware that Trump was in Moscow in 2013 for the Miss Universe pageant when it has been previously reported that Trump invited him to attend.
Putin declined but, according to the Post, he did send "a 'friendly' letter and a gift of a Russian lacquered box" to Trump.
Trump's 2013 trip to Moscow is only the tip of a Titanic-size iceberg.
As Jonathan Chait writes in New York magazine, Trump's ties to Russia stretch back to 1987 and include extensive financial connections.
Chait suggests that Trump may have been compromised by the KGB, to which Putin once belonged.
The speculation, while hardly conclusive, is entirely reasonable.
In the past week I have asked two senior, retired US intelligence officers who spent most of their careers focused on Russia how they would characterise the Putin-Trump relationship. Independently of each other, they both said, "Putin has something on Trump."
Every week lends further credence to that disturbing hypothesis.
Chait wrote before Special Counsel Robert Mueller unsealed his indictment against 12 Russian GRU military intelligence officers who hacked into Democratic Party emails as part of Moscow's effort to help elect Trump. (Putin admitted today that he favoured Trump.)
The Russians, we now know, began hacking Hillary Clinton's private servers on the very day, July 27, 2016, that Trump invited them to do so ("Russia, if you're listening").
Trump's enablers tried to dismiss his words as a big joke, but the GRU seems to have taken them as a "tasker."
The sellout in Helsinki only adds further credence to this speculation about the true nature of Trump-Putin ties. Not only did Trump fail to call out the Russian strongman for his many crimes - he also attacked the FBI and accepted Putin's assurances that Russia was not responsible for interfering in the US election even though the US intelligence community has provided overwhelming evidence that it did.
"President Putin, he just said it's not Russia," Trump said. "I will say this: I don't see any reason why it would be."
We are past the point when such statements can be dismissed as naivete - especially when Trump has previously admitted that Russia did hack the election.
We are past the point where Trump's conduct can be ascribed to his belief that it is imperative to improve US-Russia relations.
If Trump doesn't care about the state of US-German relations, US-Canadian relations or US-UK relations - all of which he has damaged in the past month - why would he care about US relations with a country that has one-fourteenth of America's GDP and one-tenth of its defence budget?
We are past the point where Trump's conduct can be ascribed to his general sympathy for dictators. If he is waging a trade war on China's dictator, why is he cosying up to Russia's dictator?
We are past the point when Trump's conduct - which leaves future elections wide open to Russian manipulation - can be ascribed to his unwillingness to do anything that will tarnish his glorious victory. It is true but insufficient to point out that that Trump's unwillingness to acknowledge the Russian attack on America is putting his own interests above the country's.
Even if Trump were thinking only in terms of his own political survival - his usual mode - he would be tougher on Putin, because he must realise that kowtowing to the Russian only strengthens suspicions of collusion. But Trump just cannot bring himself to do it.
Is that because he hopes for more aid from Putin in the future - or because he is afraid of what Putin can reveal about him? Either way, he gives every impression of betraying his oath of office.
US Constitution, Article III, Section 3: "Treason against the United States, shall consist only in levying war against them, or in adhering to their enemies, giving them aid and comfort."
Trump's own national security adviser said the Russian election attack constituted an "act of war."
So what does that make his boss?
Some - including former CIA director John Brennan - now dare call it treason.
That conclusion was once unthinkable. No longer.
